Movement (e.g., flexion and extension) of the natural human knee involves movements of the femur and the tibia. Specifically, during flexion and extension, the distal end of the femur and the proximal end of the tibia articulate relative to one another through a series of complex movements. Damage (e.g., trauma) or disease can deteriorate the bones, articular cartilage, and ligaments of the knee, which can ultimately affect the ability of the natural knee to function in such a manner. As a result, knee prostheses have been developed and implanted into surgically prepared ends of the femur and tibia.
A typical knee prosthesis for a total knee replacement includes, for example, a tibial component or tibial tray coupled to the patient's tibia, a femoral component coupled to the patient's femur, and a bearing component (or tibial insert) positioned between the tibial tray and the femoral component and including a bearing surface to accommodate the condyles of the femoral component. In some situations, it may be desirable that the tibial insert rotate relative to the tibial tray. Such rotation more closely replicates the motion of the patient's natural anatomy. In other cases, however, it may be desirable to prevent the tibial insert from rotating relative to the tibial tray. For example, various ligaments that support the knee may be compromised or damaged. In such a case, rotation of the tibial insert relative to the tibial tray may create an unstable knee. As such, a surgeon will decide on a case-by-case basis whether to use a rotating or non-rotating (fixed) tibial assembly.
Although all-polymer tibial components are available, commonly used tibial trays and tibial bearing components generally are designed so that the bearing component, whether fixed or rotating, is supported on a solid metal tray surface. The thickness of such an assembly of a tibial tray and bearing will require the removal of a certain amount of bone from the proximal tibia. Since preservation of healthy native bone is desirable in total knee replacement surgery, it is desirable to minimize the amount of bone required to be removed to accommodate the thickness of the tibial component. On the other hand, maintaining adequate properties of the tibial bearing requires that the bearing have some minimal thickness. Accordingly, it is desirable to provide a knee prosthesis system where the thickness of the tibial implant component is decreased while maintaining adequate thickness of the polymer bearing component.
In addition, it is desirable to provide a knee prosthesis system that allows for intraoperative flexibility in selecting the appropriate size and type (fixed or mobile) of components after the bone surface has been prepared.